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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 4306 (ref. '2') (Obsoleted by RFC 5996) -- Obsolete informational reference (is this intentional?): RFC 3775 (ref. '3') (Obsoleted by RFC 6275) Summary: 2 errors (**), 0 flaws (~~), 2 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group V. Devarapalli 3 Internet-Draft WiChorus 4 Intended status: Standards Track K. Weniger 5 Expires: September 10, 2009 March 9, 2009 7 Redirect Mechanism for IKEv2 8 draft-ietf-ipsecme-ikev2-redirect-05.txt 10 Status of this Memo 12 This Internet-Draft is submitted to IETF in full conformance with the 13 provisions of BCP 78 and BCP 79. This document may not be modified, 14 and derivative works of it may not be created, except to format it 15 for publication as an RFC or to translate it into languages other 16 than English. 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF), its areas, and its working groups. Note that 20 other groups may also distribute working documents as Internet- 21 Drafts. 23 Internet-Drafts are draft documents valid for a maximum of six months 24 and may be updated, replaced, or obsoleted by other documents at any 25 time. It is inappropriate to use Internet-Drafts as reference 26 material or to cite them other than as "work in progress." 28 The list of current Internet-Drafts can be accessed at 29 http://www.ietf.org/ietf/1id-abstracts.txt. 31 The list of Internet-Draft Shadow Directories can be accessed at 32 http://www.ietf.org/shadow.html. 34 This Internet-Draft will expire on September 10, 2009. 36 Copyright Notice 38 Copyright (c) 2009 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents in effect on the date of 43 publication of this document (http://trustee.ietf.org/license-info). 44 Please review these documents carefully, as they describe your rights 45 and restrictions with respect to this document. 47 Abstract 49 IKEv2 is a protocol for setting up VPN tunnels from a remote location 50 to a gateway so that the VPN client can access services in the 51 network behind the gateway. Currently there is no standard mechanism 52 specified that allows an overloaded VPN gateway or a VPN gateway that 53 is being shut down for maintenance to redirect the VPN client to 54 attach to another gateway. This document proposes a redirect 55 mechanism for IKEv2. The proposed mechanism can also be used in 56 Mobile IPv6 to enable the home agent to redirect the mobile node to 57 another home agent. 59 Table of Contents 61 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 62 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 63 3. IKEv2 Exchange with Redirect . . . . . . . . . . . . . . . . . 4 64 4. Use of Anycast Addresses with the Redirect Mechanism . . . . . 5 65 5. Gateway Initiated Redirect . . . . . . . . . . . . . . . . . . 6 66 6. Redirect Messages . . . . . . . . . . . . . . . . . . . . . . 7 67 6.1. REDIRECT_SUPPORTED . . . . . . . . . . . . . . . . . . . . 7 68 6.2. REDIRECT . . . . . . . . . . . . . . . . . . . . . . . . . 8 69 6.3. REDIRECTED_FROM . . . . . . . . . . . . . . . . . . . . . 9 70 7. Use of the Redirect Mechanism between IKEv2 Peers . . . . . . 10 71 8. Security Considerations . . . . . . . . . . . . . . . . . . . 10 72 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 73 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11 74 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 75 11.1. Normative References . . . . . . . . . . . . . . . . . . . 11 76 11.2. Informative References . . . . . . . . . . . . . . . . . . 11 77 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12 79 1. Introduction 81 IKEv2 [2] is used for setting up IPsec-based VPNs. The IP address of 82 the VPN gateway can be configured on the VPN client. But this does 83 not scale well, when the number of VPN gateways is large. Dynamic 84 discovery of VPN gateways using DNS is quite widely used too. 85 However, using DNS is not flexible when it comes to assigning a VPN 86 gateway to the VPN client based on the load on the VPN gateways. The 87 VPN client typically tries to connect to the IP address of the VPN 88 gateways that appears first in the DNS response. If the VPN tunnel 89 setup fails, then the VPN client tries to attach to the other VPN 90 gateways returned in the DNS response. 92 This document proposes a redirect mechanism for IKEv2 that enables a 93 VPN gateway to redirect the VPN client to another VPN gateway, for 94 example, based on the load condition. The redirect can be done 95 during during the IKE_SA_INIT or the IKE_AUTH exchange. Gateway- 96 initiated redirect in the middle of a session is also supported. The 97 redirect mechanism can also be used in conjunction with anycast 98 addresses. In this case, anycast address for the cluster of VPN 99 gateways is stored in the DNS instead of a list of unicast IP 100 addresses of the VPN gateways. 102 The redirect can also happen because of administrative or optimal 103 routing reasons. This document does not attempt to provide an 104 exhaustive list of reasons for redirecting a VPN client to another 105 VPN gateway. 107 Mobile IPv6 [3] may use IKEv2 for mutual authentication between the 108 mobile node and the home agent. IKEv2 may also be used for home 109 address configuration and setting up IPsec security associations for 110 protecting Mobile IPv6 signaling messages [4]. The IKEv2 exchange 111 precedes the exchange of Mobile IPv6 signaling messages. Therefore 112 the mechanism described in this document can be also be used by a 113 Mobile IPv6 home agent to redirect a mobile node to another home 114 agent. 116 There is a Home Agent Switch mechanism available for redirecting a 117 mobile node to another home agent, described in [5]. The Home Agent 118 Switch mechanism can only be used after the binding cache had been 119 created at the home agent for the mobile node. The disadvantage with 120 this is that quite a bit of state is created on the home agent before 121 the mobile node can be redirected to another home agent. The 122 mechanism described in this document can be used for redirecting a 123 mobile node before any state related to the Mobile IPv6 binding is 124 created on the home agent. 126 2. Terminology 128 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 129 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 130 document are to be interpreted as described in [1]. 132 3. IKEv2 Exchange with Redirect 134 To redirect an IKEv2 session to another VPN gateway, the VPN gateway 135 that initially received the IKE_SA_INIT request selects another VPN 136 gateway and responds to the VPN client with a REDIRECT Notification 137 payload. The mechanism by which the initial VPN gateway selects 138 another VPN gateway is out of scope for this document. The IP 139 address of the selected VPN gateway is sent in the REDIRECT payload. 141 The VPN client indicates support for the IKEv2 redirect mechanism by 142 including a REDIRECT_SUPPORTED notification message in the initial 143 IKE_SA_INIT request. If the IKE_SA_INIT request did not include the 144 REDIRECT_SUPPORTED payload, the responder MUST NOT send the REDIRECT 145 payload to the VPN client. 147 Initiator Responder (initial VPN GW) 148 --------- ------------------------- 150 (IP_I:500 -> Initial_IP_R:500) 151 HDR(A,0), SAi1, KEi, Ni, --> 152 N(REDIRECT_SUPPORTED) 154 (Initial_IP_R:500 -> IP_I:500) 155 <-- HDR(A,0), N(REDIRECT, IP_R) 157 When the VPN client receives the IKE_SA_INIT response with the 158 REDIRECT payload, it initiates a new IKE_SA_INIT exchange with the 159 VPN gateway listed in the REDIRECT payload. The VPN client includes 160 the IP address of the original VPN gateway that redirected the 161 client. The IKEv2 exchange then proceeds as normal with the selected 162 VPN gateway. 164 Initiator Responder (Selected VPN GW) 165 --------- --------------------------- 167 (IP_I:500 -> IP_R:500) 168 HDR(A,0), SAi1, KEi, Ni, --> 169 N(REDIRECTED_FROM, Initial_IP_R) 171 (IP_R:500 -> IP_I:500) 172 <-- HDR(A,B), SAr1, KEr, Nr,[CERTREQ] 174 (IP_I:500 -> IP_R:500) 175 HDR(A,B), SK {IDi, [CERT,] [CERTREQ,] 176 [IDr,]AUTH, SAi2, TSi, TSr} --> 178 (IP_R:500 -> IP_I:500) 179 <-- HDR(A,B), SK {IDr, [CERT,] AUTH, 180 SAr2, TSi, TSr} 182 When this mechanism is used with Mobile IPv6, a mobile node's 183 security associations with its home agent may expire while it still 184 has a valid binding cache entry at the home agent. In this case, the 185 mobile node MUST NOT use the original home agent address as the 186 destination address in the IKE_SA_INIT exchange to setup new security 187 associations. It MUST try to setup security associations with its 188 existing home agent. 190 4. Use of Anycast Addresses with the Redirect Mechanism 192 The use of anycast addresses will avoid having to configure a 193 particular VPN gateway's IP address in the DNS. Instead, the anycast 194 address that represents the group of VPN gateways is stored in the 195 DNS. When the VPN client performs a DNS lookup for the VPN gateway, 196 it receives the anycast address of the VPN gateway in the DNS 197 response. 199 If an anycast address is returned in response to DNS resolution of an 200 FQDN, the VPN client sends the IKE_SA_INIT request to the anycast 201 address. The IKE_SA_INIT request is routed to one of the VPN 202 gateways that is part of the anycast group. The VPN gateway that 203 receives the IKE_SA_INIT request responds with an IKE_SA_INIT reply 204 from the anycast address. 206 Initiator Responder (any VPN GW) 207 --------- ------------------------- 209 (IP_I:500 -> ANYCAST:500) 210 HDR(A,0), SAi1, KEi, Ni) --> 211 N(REDIRECT_SUPPORTED) 213 (ANYCAST:500 -> IP_I:500) 214 <-- HDR(A,0), N(REDIRECT, IP_R) 216 If the destination address on the IKE_SA_INIT request is an anycast 217 address, the VPN gateway that received the IKE_SA_INIT request MUST 218 include the REDIRECT payload to redirect the VPN client to a unicast 219 address of one of the VPN gateway. The VPN gateway that received the 220 IKE_SA_INIT request MAY redirect the client to its own unicast 221 address, if it is not overloaded. 223 The rest of the IKEv2 exchange is the same as described in Section 3. 225 5. Gateway Initiated Redirect 227 The redirect mechanism may also be used by a VPN gateway to redirect 228 the client to another VPN gateway in middle of a session. To 229 redirect a client, the gateway should send an INFORMATIONAL message 230 with the REDIRECT Notify payload. The REDIRECT payload MUST carry 231 information about the new VPN gateway. When the client receives this 232 message, it MUST send an empty message as an acknowledgement. Until 233 the client responds with an acknowledgement, the gateway SHOULD re- 234 transmit the redirect INFORMATIONAL message as described in [2]. The 235 following illustrates the INFORMATIONAL message exchange for gateway- 236 initiated redirect. 238 Initiator (VPN client) Responder (VPN GW) 239 ---------------------- ------------------ 241 <-- HDR, SK {N[REDIRECT, IP_R/FQDN_R]} 243 HDR, SK {} --> 245 The INFORMATIONAL message exchange described above is protected by 246 the existing IKEv2 SA between the client and the gateway. 248 Once the client sends an acknowledgement to the gateway, it SHOULD 249 delete the existing security associations with the old gateway by 250 sending an Informational message with a DELETE payload. The gateway 251 MAY also decide to delete the security associations without any 252 signaling from the client, again by sending an Informational message 253 with a DELETE payload. However, it should allow sufficient time for 254 the client to setup the required security associations with the new 255 security gateway. This time period should be configurable on the 256 gateway. 258 If the gateway decides to redirect the client during the IKE_AUTH 259 exchange, it prevents the creation of a CHILD SA by sending the 260 NO_ADDITIONAL_SAS Notify Payload in the IKE_AUTH response. It then 261 follows up with an INFORMATIONAL message with the REDIRECT payload 262 immediately. The following shows the message exchange between the 263 client and the gateway. 265 Initiator Responder ( VPN GW) 266 --------- ------------------- 268 (IP_I:500 -> IP_R:500) 269 HDR(A,0), SAi1, KEi, Ni, --> 270 N(REDIRECTED_SUPPORTED) 272 (IP_R:500 -> IP_I:500) 273 <-- HDR(A,B), SAr1, KEr, Nr,[CERTREQ] 275 (IP_I:500 -> IP_R:500) 276 HDR(A,B), SK {IDi, [CERT,] [CERTREQ,] 277 [IDr,]AUTH, SAi2, TSi, TSr} --> 279 (IP_R:500 -> IP_I:500) 280 <-- HDR(A,B), SK {IDr, [CERT,] AUTH, 281 N(NO_ADDITIONAL_SAS)} 283 <-- HDR, SK {N[REDIRECT, IP_R/FQDN_R]} 285 HDR, SK {} --> 287 When the client receives the IKE_AUTH response with the 288 NO_ADDITIONAL_SAS payload from the gateway, it may decide to delete 289 the IKEv2 SA. In case the gateway receives the INFORMATIONAL message 290 to delete the IKEv2 SA before sending the REDIRECT message, then the 291 gateway includes the REDIRECT payload in the response along with the 292 DELETE payload. 294 6. Redirect Messages 296 6.1. REDIRECT_SUPPORTED 298 The REDIRECT_SUPPORTED payload is included in the initial IKE_SA_INIT 299 request by the initiator to indicate support for the IKEv2 redirect 300 mechanism described in this document. 302 1 2 3 303 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 304 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 305 | Next Payload |C| RESERVED | Payload Length | 306 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 307 | Protocol ID | SPI Size (=0) | Notify Message Type | 308 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 310 The 'Next Payload', 'Payload Length', 'Protocol ID', 'SPI Size' and 311 the 'Notify Message Type' fields are the same as described in Section 312 3.10 of [2]. The 'SPI Size' field MUST be set to 0 to indicate that 313 the SPI is not present in this message. The 'Protocol ID' should be 314 set to 0, since the notification is not specific to a particular 315 security association. 317 The 'Payload Length' field MUST be set to '8'. The 'Notify Message 318 Type' field is set to indicate the REDIRECT_SUPPORTED payload . 321 6.2. REDIRECT 323 The REDIRECT payload is included in an IKE_SA_INIT response from the 324 responder or an INFORMATIONAL message from the responder, when the 325 responder wants to redirect the initiator to another VPN gateway. 326 The message includes the new responder's IP address. 328 1 2 3 329 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 330 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 331 | Next Payload |C| RESERVED | Payload Length | 332 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 333 | Protocol ID | SPI Size (=0) | Notify Message Type | 334 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 335 | GW Ident Type | | 336 +---------------+ ~ 337 ~ New Responder GW Identity ~ 338 | | 339 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 341 The 'Next Payload', 'Payload Length', 'Protocol ID', 'SPI Size' and 342 the 'Notify Message Type' fields are the same as described in Section 343 3.10 of [2]. The 'SPI Size' field MUST be set to 0 to indicate that 344 the SPI is not present in this message. The 'Protocol ID' should be 345 set to 0, since the notification is not specific to a particular 346 security association. 348 If the IP address of the new VPN gateway is sent, the 'Payload 349 Length' field MUST be set to either '13' or '25' depending on whether 350 an IPv4 or IPv6 address is sent in the message. If the FQDN of the 351 new VPN gateway is sent, the 'Payload Length' field is set to the 352 length of the FQDN plus the fixed fields in the message. The 'Notify 353 Message Type' field is set to indicate the REDIRECT payload . The 'GW Identity Type' field indicates the 355 type of information that is sent to identify the new VPN gateway. 356 The following values are reserved by this document. 358 1 - IPv4 address of the new VPN gateway 359 2 - IPv6 address of the new VPN gateway 360 3 - FQDN of the new VPN gateway 362 All other values for this field are reserved and MUST NOT be used. 363 The identity of the new VPN gateway is carried in the 'New Responder 364 GW Identity' field. 366 6.3. REDIRECTED_FROM 368 The REDIRECTED_FROM message type is included in the IKE_SA_INIT 369 request from the initiator to the new VPN gateway to indicate the IP 370 address of the original VPN gateway that redirected the initiator. 371 The original VPN gateway's IP address is included in the message. 373 1 2 3 374 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 375 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 376 | Next Payload |C| RESERVED | Payload Length | 377 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 378 | Protocol ID | SPI Size (=0) | Notify Message Type | 379 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 380 | GW Ident Type | | 381 +---------------+ ~ 382 ~ Original Responder GW Identity ~ 383 | | 384 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 386 The 'Next Payload', 'Payload Length', 'Protocol ID', 'SPI Size' and 387 the 'Notify Message Type' fields are the same as described in Section 388 3.10 of [2] The 'SPI Size' field MUST be set to 0 to indicate that 389 the SPI is not present in this message. The 'Protocol ID' should be 390 set to 0, since the notification is not specific to a particular 391 security association. 393 The 'Payload Length' field MUST be set to either '13' or '25' 394 depending on whether an IPv4 or IPv6 address of the original VPN 395 gateway is sent in the message. The 'Notify Message Type' field is 396 set to indicate the REDIRECTED_FROM payload . The 'GW Identity Type' field indicates the type of 398 information that is sent to identify the new VPN gateway. The 399 following values are reserved by this document. 401 1 - IPv4 address of the original VPN gateway 402 2 - IPv6 address of the original VPN gateway 404 All other values for this field are reserved and MUST NOT be used. 405 The identity of the original VPN gateway is carried in the 'Original 406 Responder GW Identity' field. 408 7. Use of the Redirect Mechanism between IKEv2 Peers 410 The Redirect mechanism described in this document is mainly intended 411 for use in client-gateway scenarios. However, the mechanism can also 412 be used between any two IKEv2 peers. But this protocol is 413 asymmetric, meaning that only the original responder can redirect the 414 original initiator to another server. 416 8. Security Considerations 418 An eavesdropper on the path between VPN client and server may send a 419 redirect to the client upon receiving an IKE_SA_INIT message from 420 this client. This is no problem regarding DoS attacks for the VPN 421 connection, since an on-path-attacker can as well drop the 422 IKE_SA_INIT requests to prevent VPN access for the client. But an 423 eavesdropper on the path between VPN client and server can redirect a 424 large number of clients to a victim, which is then flooded with 425 IKE_SA_INIT requests. Flooding only happens if many clients initiate 426 IKEv2 exchange at almost the same time, which is considered a rare 427 event. However, this may happen if a Home Agent/VPN server is 428 shutdown for maintenance and all clients need to re-establish VPN 429 connections with another Home Agent/VPN server or if the on-path 430 attacker forces all IPsec security associations to expire by dropping 431 all received IKEv2 messages. 433 The use of REDIRECTED_FROM payload is intended to discourage a rogue 434 VPN gateway from redirecting a large number of VPN clients to a 435 particular VPN gateway. It does not prevent such a DoS attack. 437 9. IANA Considerations 439 This document defines four new IKEv2 Notification Message types as 440 described in Section 6. The three Notify Message Types must be 441 assigned values between 16396 and 40959. 443 o REDIRECT_SUPPORTED 444 o REDIRECT 445 o REDIRECTED_FROM 447 10. Acknowledgements 449 The use of anycast address with IKEv2 was first described in [6]. It 450 was then added to an early draft version of RFC 5026 and later 451 removed before the RFC was published. Therefore the authors of [6] 452 and RFC 5026 are acknowledged. 454 Thanks to Pasi Eronen, with whom the solution described in this 455 document was extensively discussed. Thanks to Tero Kivinen for 456 suggesting the use of REDIRECTED_FROM payload and other comments 457 which helped improve the document. The authors would also like to 458 thank Yaron Sheffer, Sunil Kumar, Fan Zhao, Yoav Nir, Richard 459 Graveman, and Arnaud Ebalard for their reviews and comments. 461 11. References 463 11.1. Normative References 465 [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement 466 Levels", BCP 14, RFC 2119, March 1997. 468 [2] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", RFC 4306, 469 December 2005. 471 11.2. Informative References 473 [3] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in 474 IPv6", RFC 3775, June 2004. 476 [4] Giaretta, G., Kempf, J., and V. Devarapalli, "Mobile IPv6 477 Bootstrapping in Split Scenario", RFC 5026, October 2007. 479 [5] Haley, B., Devarapalli, V., Deng, H., and J. Kempf, "Mobility 480 Header Home Agent Switch Message", RFC 5142, January 2008. 482 [6] Weniger, K. and F. Dupont, "IKEv2-based Home Agent Assignment in 483 Mobile IPv6/NEMO Bootstrapping", draft-dupont-ikev2-haassign-02 484 (work in progress), January 2007. 486 Authors' Addresses 488 Vijay Devarapalli 489 WiChorus 490 3590 North First St 491 San Jose, CA 95134 492 USA 494 Email: vijay@wichorus.com 496 Kilian Weniger 498 Email: kilian.weniger@googlemail.com